1. Field of the Invention
This invention relates generally to cardiopulmonary test apparatus, and more particularly to a low-cost, single-use, multifunction patient valve for use in such equipment.
2. Discussion of the Prior Art
A variety of medical diagnostic equipment is available in the marketplace for measuring and assessing cardiopulmonary performance. The Anderson et al. U.S. Pat. No. 4,463,764 assigned to Medical Graphic's Corporation applicant's assignee, describes a computer-based system capable of measuring certain parameters on a breath-by-breath basis and for computing and presenting most of the important parameters for assessing cardiopulmonary performance.
A more recent system available from Medical Graphics Corporation is described in the Snow et al. U.S. Pat. No. 4,796,639. This system includes lung measurement equipment for providing data to a computer during testing of the patient. For example, a volume measuring device such as a body plethysmograph provides an input relating to slow vital capacity, residual volume, thoracic gas volume, total lung capacity, and alveolar volume. Equipment is also available for measuring respiratory gas flow, allowing a determination of forced vital capacity, forced expiratory volume and related flow parameters to be measured. In addition, that system permits diffusion measurements so that the ability of the lungs to transfer gas can be assessed. Respiratory pressure is also a meaningful parameter in diagnostic work.
Equipment of the type described requires a patient to inhale and exhale in a controlled fashion as normal air or other gases are introduced. For example, when conducting the diffusion testing, the patient is first asked to exhale as completely as possible and then a suitable gas mixture, such as CO and Neon in air, is inspired from a gas source. Following inspiration, the patient is made to hold his breath for a precise time period during which the CO gas is being absorbed by the blood through the lung tissue. Following that prescribed time interval, the patient exhales into a sample tube. Knowing the amount of CO initially inhaled and the amount finally exhaled to the sample tube allows a computation to be made of the amount of gas transferred through the lungs to the blood. A measurement of the dilution of Neon which does not diffuse through the lung tissue can be used to determine alveolar volume.
A related procedure called nitrogen washout is used to actually assess a patient's lung volume. Here, a patient is made to breathe air normally and then the air supply is blocked and pure oxygen is made available through a demand valve. The patient continues to breathe pure oxygen for period of time sufficient to eliminate all nitrogen from the expired breath. By measuring the total amount of nitrogen gas expired during this interval, lung volume can be assessed in that it is known what the proportion of nitrogen is in normal air in the lungs at a given pressure and temperature.
The device used to control the routing of inspired and expired air and/or other gases in the desired manner for accomplishing the diffusion test and the nitrogen washout test involves the use of a so-called patient valve. When it is recognized that the given patient must both inhale and exhale through the patient valve, there is a need for ensuring that cross-contamination between successive patients using the equipment is eliminated. Because, in the past, such patient valves tend to be quite complex and therefore costly, it has been impractical to treat them as a disposable item. Moreover, prior art valve systems have required cumbersome cleaning operations involving disassembly and reassembly and have been difficult to clean and/or completely sterilize between uses.
Jaeger Medical Instruments of Rockford, Illinois offers a system which it refers to as the "MasterLab" multi-purpose diffusion testing system. It incorporates a specially designed patient valve block that it advertises as being fully sterilizable. Because of complexities, it cannot economically be treated as a "disposable." It comprises a plastic block having a series of interconnected bores formed therein along with appropriate shutters and seals to effect gas routing in a desired fashion. To adequately sterilize the device requires the submersion of the valve assembly in a sterilent for a predetermined time, followed by drying and reinstallation into the test equipment. This necessarily limits the availability of the equipment in running tests on a series of patients and is wasteful of professional time.
Another manufacturer of patient valves is Hans Rudolph, Inc. Its Model 4200 pneumatic mouthshutter and its line of directional control valves, for example, involves relatively costly precision parts including pneumatic actuated pistons, seals and balloon valve assemblies. It cannot be autoclaved and must be disassembled to allow exposure to gas or cold liquid sterilents.
It is accordingly a principle object of the present invention to provide an improved patient valve for use in the cardiopulmonary test equipment.
Another object of the invention is to provide a patient valve which can be manufactured at sufficiently low cost that it can be discarded after a single use.
Still another object of the invention is to provide a replaceable patient valve which can readily be installed in cardiopulmonary performance analyzing equipment by semi-skilled personnel rapidly and reliably so as not to impair the quality of the measurements being taken.
Yet another object of the present invention is to provide a patient valve that obviates the need for any filters to prevent patient cross-examination, thus maintaining unrestricted gas flow through the valve body when the valve structure is "open".